diff --git a/sections/event-wheelevent.txt b/sections/event-wheelevent.txt
index 0c773e8..de71fa5 100644
--- a/sections/event-wheelevent.txt
+++ b/sections/event-wheelevent.txt
@@ -163,6 +163,21 @@
 					The <a>un-initialized value</a> of this attribute MUST be
 					<code>0</code>.
 				</dd>
+
+				<dt><dfn attribute>source</dfn></dt>
+				<dd>
+					The <code>source</code> attribute is a ready only attribute which
+					indicates the reason this event has been generated and takes one of
+					three possible values:
+
+					  * 'user': this event has been generated as a result of direct user
+					    action.
+					  * 'momentum': this event has been generated as a result of momentum
+					    scrolling which is an animation that is done after the user stops
+					    directly interacting with the input device.
+					  * 'unknown': the browser could not determine the reason this event
+					    has been generated
+				</dd>
 			</dl>
 
 		<h5 id="idl-wheeleventinit">WheelEventInit</h5>
@@ -265,6 +280,8 @@
 			 |                  |     value of movement of a wheel around the z-axis</li>                              |
 			 |                  | <li>{{WheelEvent}}.{{WheelEvent/deltaMode}} : unit indicator (pixels, lines, or      |
 			 |                  |     pages) for the deltaX, deltaY, and deltaZ attributes</li>                        |
+			 |                  | <li>{{WheelEvent}}.{{WheelEvent/source}} : source of this event (e.g. user or        |
+			 |                  |     momentum).</li>                                                                  |
 			 |                  | </ul>                                                                                |
 			++------------------+--------------------------------------------------------------------------------------+